The present invention relates to a method of operating a pneumatic brake power booster including a movable wall and a control valve controlling a pneumatic pressure differential which acts upon the movable wall, the control valve having at least two sealing seats and an elastic valve member which interacts with the sealing seats, and, on the one hand, being operable by the driver by way of an actuating rod and, on the other hand, by a solenoid which is in a force-transmitting connection with one of the sealing seats.
German patent application No. 43 24 688 discloses a brake power booster for implementing a method of this type. The brake power booster is operable electromechanically irrespective of the driver's wish, i.e. of a brake pedal actuation. The special characteristics of the prior art brake power booster include sensor elements which permit identification of the valve member of the control valve in order to achieve a controlled proportioning of the independent actuating force to be generated by the solenoid. Further, an information about the travel covered during the control process by the electromechanically operable sealing seat is required for the control. This necessitates further sensor elements including the associated electronics.
However, the use of the mentioned sensor means involves a considerable amount of costs.
The article "Electronically Controlled Brake Power Booster" published in the Automobile Technology Journal ATZ 97 (1995) January, No.1, pages 36-37, describes an electrically operable booster with a proportional control. The control valve of the booster is drivable by a proportional electromagnet. A disadvantage in the mentioned booster is the comparatively high weight of the proportional magnet and the related increased overall dimensions of the booster. Another disadvantage is the relatively exact control which is assessed as costly.
Therefore, an object of the present invention is to disclose a method of the previously mentioned type which, when implemented, obviates the need for any additional sensor means and can be achieved at low cost with already provided parts. Another objective is to extend the control range predetermined due to tolerances.